Process of recovering zinc from sulfid ores.



PATENTED DEC. 15, 1903.

V P. DANGKWARDT. PROCESS OF RFJEOVERINGr ZINC PROM SULPID ORBS.

FIG- 2..

APPLICATION FILED AUG. 15, 1903.

No. 746.798. no MODEL.

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I a 176 4 A 7 m: u uwms Pcl'r wfr/a. mm uruo ASHINGY D c UNIT D STATESPatented. December 15, 1903.

PATENT OFFICE.

PAUL DANOKWARDT, OF DEADWOOD, SOUTH DAKOTA.

SPECIFIGATIONformiug part 'of Letters Patent No. 746,798, dated December1 5, 1903.

Application filed Angust'lfi, 1903. Serial No. 169,560? (No specimens.)

To all whom, it may concern:

Be it known that 1, PAUL DANCKWABDT, a citizen of the United States,residing at Deadwood, Lawrence county, South Dakota, have inventedcertain new and useful Improvements in Processes of Recovering Zinc andthose carrying lead-zinc sulfid, the copperzinc sulfid, zinc sulfidpure, such concentrates from the above classes of ore as are too low invalue for a direct treatment, and furnace products of a similarconstitution, such as flue-dust, matte, &c. All these ores may or maynot contain gold or silver.

The process, briefly stated, consists in heating electricallya mixtureof the ore, &c., with a salt'of an alkali metal and a carbid of anymetal or a carbid-forming material and sufficient fluxes to slag off theimpurities of the main the presence of a large excess of carbon. In theaccompanying drawings, Figure l is a vertical longitudinal section of anapparatus for carrying myinvention into efiect, and Fig. 2 across-section on line 2 2, Fig. l.

The letter a represents a retort the walls of which rest on a refractoryfoundation 1), having an inclined top. The retort a is cooled bywater-jackets c, which are provided with bon block j, that projects intothe retortf The manhole 2' has a cover t and is designed for theintroduction of charcoal or coke. A second carbon block it isintroducedthrough a perforation in the side of the retort and issupported within a -surface groove of foundation 1). The carbon blocks jk are insulated from the retort and connected by wires 7" It to asuitable source of electricity. The retort o; communicates near its topby a condensingpipe Z with a closed receptacle m. This receptacle has asmall outlet-pipe n for the escape of the gases formed. Near its lowerend the retort has a tap-hole o with spout 0.

In carrying out my invention I mix the dried ore with fluxes and suchamounts of an alkali salt and carbid or carbid-forming materials thatall the sulfur combined with the zinc, lead, or copper of the ore willfind sufficient alkali metal to combine therewith when the charge isheated. This mixture is introduced into the retort through shaft 9 andis covered by coke or another carbon compound introduced through manholet. The current is then turned into the carbon blocksj it, so that thecharge is subjected to heat, while air is excluded. if iron pyrites bepresent, the ores should be treated with such proportions of alkali saltand carbid-forming materials and fluxes as to withdraw-the sulfur fromthe metals to be obtained in a free state and so much of the sulfur ofthe iron pyrites as to transform the latter into iron matte and form afluid slag. The fluxes to be used with the process are such as will forma fluid slag with the silica and other gangue contained in the ore. Toillustrate, I will assume an ore of the following constitution:

If the iron persulfid (FeS is to be reduced only to the state of ironsulfid, (FeS,) which is a compound that will stand fusion without.further decomposition, it will deliver one The reaction runs probablyso that first the too , quire one molecule of calcium carbonate to forma good fluid slag. Thus the total reaction in this special case would betifiitfltitfiett fittfi diiaigfi823F560. Numerically expressed,theproportionsin this special case would be, by weight, taking intoconsideration the usual impurities of the materials, six hundred andeighty-three parts of the above ore, six hundred parts of sodiumsulfate, five hundred and fifty parts of limestone, and three hundredand thirty parts of coke. In practice I add about double this quan tityof coke or the corresponding amount of other carbon compound in order toprevent the formation or to cause the reduction of any carbon dioxidformed, which when escaping, together with the vapors of zinc, wouldcause a partial oxidation of the latter. To make absolutely sure thatsuch an oxidation cannot take place, I fill the retort through themanhole 'i with charcoal or coke in pieces, so that the fusion of thecharge coming down the shaft toward the carbon poles takes place under aheavy cover of glowing carbon.

As carbid-forming materials I prefer to use limestone or iron ore andcoke or coal; but

.alumina (clay) or magnesia or any compound forming a ,carbid under theconditions described will do just as well. I prefer sodium sulfate,though any other salt of the alkali metals will give good results.

The above formula and proportions refer only to a special case and showin what manner the amounts of alkali salt, carbid-forming materials, andfluxes have to be proportioned to the quantities of the singleingredients of the ore. Any arsenic, if present, may be figured astaking the place of sulfur.

The above reactions will set in as soon as the current has producedsufficient heat. The mass will gradually melt and become so hot that thereduced metals will part from the rest of the charge. The zinc, asthemost volatile metal, will rise in fumes and is condensed by passingthrough the pipe Z, which discharges it in a molten state into thereceptacle m. Any carbon oxid formed will escape through pipe n. Theother metals, which contain all the gold and silver of the charge whenpresent, will run down the inclined bottom of the furnace. They areremoved by tapping them from spout o, together with the slag and thesulfids of sodium and calcium and whatever iron matte is formed. Themetals and matte are allowed to settle out, and the slag and sulfids arede- As an alkali salt tached from them after all has cooled. As thecharge is thus melting away from the bottom and while it is sinking inthe shaft g new charges must be added at the top of the shaft, thusmaking the process continuous. The slag together with the sulfids arebroken up after cooling, and the sodium sulfid is leached out by water.This solution is then treated by a current of carbonic acid or gasescontaining a large percentage of carbonic-acid gas, whereby the sodiumsulfid is changed into sodium carbonate and hydrogen sulfid (H 8) isdriven off. The sodium carbonate is then recovered from the solution byevaporation or crystallization, while the hydrogen sulfid may be turnedeither into sulfur or into sulfuric acid by means of any of thewell-known methods.

It has heretofore been proposed to obtain zinc from sulfid ores bysmelting such ores with lime and carbon or iron and carbon; but bothprocesses turned out failures as long as the smelting was done withother means than the electric current, only by smelting the mixtureelectrically under exclusion of air the result is more satisfactory; butthe high temperature of from 1,500 to 3,000 centigrade required to causethe reduction of the sulfids without the addition of an alkali salt,combined with the high expenditure of power, are objectionable. Withsuch a high temperature it happens that the sulfur which has alreadycombined with calcium is again driven out by an excess of carbon, andwill thus recombine with part of the volatilizing zinc. The addition ofan alkali salt prevents this, as any carbid reforming would liberatepart of the alkali metal of the alkali sulfid, which in turn will bindthe sulfur set free. On the other hand, the reaction with the alkalisalt present takes place at a much lower temperature, whereby .thereversion of the reaction is also obviated. As it is of importance towork with a large excess of carbon in and above the charge to preventthe formation of carbon dioxid, it cannot be avoided that such backwardreaction partly sets in if lime or iron ore and carbon alone are used.The object of the alkali salt is therefore to prevent this reaction; butthere are other advantages derived from such additionviz., the greatereconomy of power and the production of sodium sulfid, which, as beforestated, can easily be worked into sodium carbonate, yielding at the sametime sulfur or sulfuric acid as by-products. This process, therefore,permits the recovery not only of the metals, but also of the sulfurcontained in the ore and utilizes the heat in a better way by formingvaluable by-products.

What I claim is l 1. The process of recovering zinc and other valuablemetals from their sulfids which consists in subjecting such sulfids tothe action of a nascent alkali metal by heating them electrically underexclusion of air with a mixture of an alkali-metal salt and a carbid ofsists in heatingelectrically such sulfide under I exclusion'of air witha mixture of sodium sulfate, a carbid of any metal or carbid-formingmaterial, lime, and an excess of carbon, substantially as specified.

4. The process of recovering and separating zinc and other valuablemetals from ores or furnace product of a similar constitution, whichconsists in mixing the dry ore with a salt of an alkali metal, a carbidof any metal I or a carbid-forming material, the carbid to be in excessover that required to bind all the oxygen of the charge in the form ofcarbon monoxid, mixing it further with fluxes for slagging of gangue andimpurities of the ore, heating this mixture electrically under a heavycover of carbon to prevent the formation of any carbon dioxid,condensing the vapors of zinc and Withdrawing the rest of the charge ina molten state, allowing the metals and matte to settle from the slagand sulfids of the alkali metal and calcium, dissolving the alkalisultid in Water, treating this solution with carbon dioxid, evaporatingor crystallizing out the alkali carbonate and. treating the escapinghydrogen sulfid for the recovery of the sulfur, substautiall y asspecifled.

Signed by me at Deadwood, Lawrence county, South Dakota, this 10th dayof August, 1903.

PAUL DANCKWARDT.

Witnesses:

J. E. FORD,

. K. W. TRIMBLE.

